The present disclosure generally relates to severing tubular structures in a downhole environment, and, more specifically, to tools and methods employing an explosive material for severing downhole tubular structures.
Modern wellbores can extend thousands of feet below the earth's surface and be several miles in overall length, particularly if the wellbore is deviated with one or more substantially non-vertical sections. In most instances, one or more tubular structures are present within a wellbore at various points during its lifecycle. Illustrative tubular structures that commonly may be present within a wellbore include, for example, casing, drill pipe, drill collars, production tubing, coiled tubing, and the like. Such tubular structures often may be used in conjunction with introducing a fluid to a particular location of a subterranean formation or with producing a fluid from a subterranean formation. Tubular structures may also provide other downhole functions.
Under ordinary operational circumstances, most tubular structures extend from the earth's surface to a location along the length of the wellbore in order to allow a well operator to manage ongoing operations therein. In some instances, various events in a wellbore can necessitate severing a tubular structure within the wellbore at a location below the earth's surface. The terms “sever” and “cut” and grammatical equivalents thereof will be used interchangeably with one another herein. The most common operational circumstance necessitating severing of a downhole tubular structure is a condition known as stuck pipe. As used herein, the term “stuck pipe” refers to a state in which a downhole tubular structure cannot be rotated, moved along the length of the wellbore, or any combination thereof. A number of events within the wellbore can lead to an occurrence of stuck pipe including, for example, collapse of a section of the wellbore wall, accidental contact of the tubular structure with an uncased section of the wellbore wall, and the like. Most significantly, stuck pipe can prevent a tubular structure from fully extending all the way from the earth's surface to an intended location within the wellbore.
One way in which rapid severing of a tubular structure may take place is through detonation of an explosive material. In performing explosive severing of a stuck pipe, the position and depth of the tubular structure in the wellbore, among other factors, can first be determined (e.g. using a wireline tool), and then a tool containing an explosive material can be lowered through the tubular structure to the measured location or above. The explosive material is then detonated to result in severance of the tubular structure. The physical size of the explosive material in the tool may be dictated by the inner diameter of the tubular structure, as well as by the volume of the tool itself. The explosive can be configured to provide brute force severing or designed cutting of the tubular structure.
Although explosive severance of a tubular structure can often be successfully accomplished, it may sometimes be the case that an explosive material having a great enough explosive yield to result in severing cannot be effectively lowered though a particular tubular structure. That is, the diameter and internal volume of a severing tool may not allow a sufficient amount of explosive material to be positioned in a tubular structure to affect its severance, for example due to downhole hydrostatic pressure and the wall thickness of the tubular structure. In this instance, there are presently few options available for a well operator to increase explosive yield.